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The update, issued on Wednesday, falsely labeled important Windows system files as potentially malign, dispatching them into quarantine. The action prevents Windows XP systems from booting properly.

A discussion thread on CA's support forum reflects widespread frustration over the problem, echoed in email tips from Reg readers.

"My phones are ringing off the hook as CA Antivirus is quarantining genuine windows files left, right and centre," writes one of our correspondents. "Anyone else ripping their hair out?"

In a statement (below), CA said it issued a revised update on Thursday that resolved the problem.

On July 8, 2009 at 11:00am EST, a CA DAT file release contained improperly formed malware detections that errantly detected clean files from Microsoft Windows Service Pack 3 and from the commercial Cygwin application. Affected files were detected as "Win32\Amalum" variants with extensions such as ZZNRA, ZZOFK, ZZNPB, and ZZNRA.

All files falsely detected as malware by these errant signatures were quarantined and renamed with the following text added to the file name "*.AVB". This prevented the affected files from running as the ".exe" file. It's important to note that the affected files remain fully intact, only the file extensions were modified.

On July 9, 2009 at 3:30am EST the file was corrected and released.

False positives involving anti-virus scanners are an industry-wide problem. Users are worst affected when, as in the current case with CA, core system files (rather than simply the components of regular applications) are labeled as potentially malign. Solving the problem involves rolling back to previous definition or issuing new updates that avoid Chicken Little-style false alarms. ®